Risk Factors

Genes that determine the angles, amount of force, and other structural factors in the hip joints, or genes that regulate the chemistry in the joints, may account for ethnic differences.

Physical and Anatomical Factors

Some researchers suggest that a number of people have anatomical abnormalities, such as mismatched surfaces on the joints, which could be damaged over time by abnormal stress. Legs of unequal length or skewed feet can cause jerky movement and may cause osteoarthritis. One study reported that those whose knees bent inward ("knock-kneed") or outward ("bow-legged"), for example, were more likely to have progressive osteoarthritis of the knee.

Obesity

Obesity, defined as being 20% over one's healthy weight, places people (particularly women) at increased risk for osteoarthritis. It also worsens osteoarthritis once deterioration begins. This higher risk is due to increased weight on the joints. However, being obese also increases the risk for osteoarthritis in the fingers as well as the knees and hips, suggesting that being overweight may contribute to osteoarthritis in other ways. Some research indicates that obesity may produce an inflammatory response, which is now a major suspect in age-related diseases -- not only osteoarthritis but also heart disease. [See In-Depth Report #53: Weight control and diet.]

Work and Leisure Factors

Because injuries can trigger the disease process, people whose work or leisure activities place them at risk for muscle and joint injuries may face a higher risk for osteoarthritis later on.

Workers at Higher Risk. Certain occupations that require repeated stressful motions (such as squatting or kneeling with heavy lifting) can contribute to deterioration of cartilage. One study suggested that workers whose jobs require kneeling or squatting for more than an hour a day are at high risk for knee osteoarthritis. (In the study, jobs that involved heaving lifting, climbing stairs, or walking also posed some, but not as high, a risk. Being heavier compounded the chances for osteoarthritis.)